In the conventional art of in vitro growth of tissues or cells, biological samples are typically fixed to the bottom of a tube or petri dish and bathed from above with nutrient solution or culture media. This arrangement does not reflect the manner in which the cells receive nutrients in vivo.
An improved tissue culture apparatus, the transwell, is described in applicant's U.S. Pat. No. 5,026,649 issued Jun. 25, 1991, the disclosure of which is incorporated herein by reference. In the Transwell.TM., the tissue sample is separated from the nutrient medium by a permeable membrane. A concentration gradient of nutrients then may develop and feed the cells through this permeable membrane, which arrangement more closely reflects to the situation in vivo. The permeable membrane is attached to the bottom end of a tubular support that in turn hangs by a flange at its upper end from the top of a well containing the nutrients. Typically, the well is part of a tissue culture dish. The flange of the support positions the support and membrane centrally in the well. Openings in the side wall of the support provided access for a pipette to add and withdraw fluid from the well.